| Age | Commit message (Collapse) | Author |
|---|
|
Currently there's a minor bug where the constant for the min fraction of
time spent scavenging is rounded down to zero. I don't think this
affects anything in practice because this case is exceedingly rare and
extreme, but currently it doesn't properly prevent the pacing parameters
from getting out of hand in these extreme cases.
Fixes #44036.
Change-Id: I7de644ab0ecac33765c337a736482a0966882780
Reviewed-on: https://go-review.googlesource.com/c/go/+/313249
Reviewed-by: Michael Pratt <mpratt@google.com>
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
|
|
This change moves next_gc and last_next_gc into gcControllerState under
the names heapGoal and lastHeapGoal respectively. These are
fundamentally GC pacer related values, and so it makes sense for them to
live here.
Partially generated by
rf '
ex . {
memstats.next_gc -> gcController.heapGoal
memstats.last_next_gc -> gcController.lastHeapGoal
}
'
except for updates to comments and gcControllerState methods, where
they're accessed through the receiver, and trace-related renames of
NextGC -> HeapGoal, while we're here.
For #44167.
Change-Id: I1e871ad78a57b01be8d9f71bd662530c84853bed
Reviewed-on: https://go-review.googlesource.com/c/go/+/306603
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
|
|
Adds code to the compiler's "order" phase to rewrite go and defer
statements to always be argument-less. E.g.
defer f(x,y) => x1, y1 := x, y
defer func() { f(x1, y1) }
This transformation is not beneficial on its own, but it helps
simplify runtime defer handling for the new register ABI (when
invoking deferred functions on the panic path, the runtime doesn't
need to manage the complexity of determining which args to pass in
register vs memory).
This feature is currently enabled by default if GOEXPERIMENT=regabi or
GOEXPERIMENT=regabidefer is in effect.
Included in this CL are some workarounds in the runtime to insure that
"go" statement targets in the runtime are argument-less already (since
wrapping them can potentially introduce heap-allocated closures, which
are currently not allowed). The expectation is that these workarounds
will be temporary, and can go away once we either A) change the rules
about heap-allocated closures, or B) implement some other scheme for
handling go statements.
Change-Id: I01060d79a6b140c6f0838d6e6813f807ccdca319
Reviewed-on: https://go-review.googlesource.com/c/go/+/298669
Trust: Than McIntosh <thanm@google.com>
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>
|
|
Change-Id: Ib689e5793d9cb372e759c4f34af71f004010c822
GitHub-Last-Rev: d63798388e5dcccb984689b0ae39b87453b97393
GitHub-Pull-Request: golang/go#44259
Reviewed-on: https://go-review.googlesource.com/c/go/+/291949
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Robert Griesemer <gri@golang.org>
|
|
recieved -> received
Change-Id: I84336170e179832604e1311ea9263af36f9ce15a
GitHub-Last-Rev: a6068c1d2b5a7711b93899f798dbc84f1ea339e4
GitHub-Pull-Request: golang/go#43845
Reviewed-on: https://go-review.googlesource.com/c/go/+/285675
Reviewed-by: Keith Randall <khr@golang.org>
Trust: Alberto Donizetti <alb.donizetti@gmail.com>
|
|
This change modifies the consistent stats implementation to keep the
per-P sequence counter on each P instead of each mcache. A valid mcache
is not available everywhere that we want to call e.g. allocSpan, as per
issue #42339. By decoupling these two, we can add a mechanism to allow
contexts without a P to update stats consistently.
In this CL, we achieve that with a mutex. In practice, it will be very
rare for an M to update these stats without a P. Furthermore, the stats
reader also only needs to hold the mutex across the update to "gen"
since once that changes, writers are free to continue updating the new
stats generation. Contention could thus only arise between writers
without a P, and as mentioned earlier, those should be rare.
A nice side-effect of this change is that the consistent stats acquire
and release API becomes simpler.
Fixes #42339.
Change-Id: Ied74ab256f69abd54b550394c8ad7c4c40a5fe34
Reviewed-on: https://go-review.googlesource.com/c/go/+/267158
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Trust: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
|
|
This change moves the responsibility of throwing if an mcache is not
available to the caller, because the inlining cost of throw is set very
high in the compiler. Even if it was reduced down to the cost of a usual
function call, it would still be too expensive, so just move it out.
This choice also makes sense in the context of #42339 since we're going
to have to handle the case where we don't have an mcache to update stats
in a few contexts anyhow.
Also, add getMCache to the list of functions that should be inlined to
prevent future regressions.
getMCache is called on the allocation fast path and because its not
inlined actually causes a significant regression (~10%) in some
microbenchmarks.
Fixes #42305.
Change-Id: I64ac5e4f26b730bd4435ea1069a4a50f55411ced
Reviewed-on: https://go-review.googlesource.com/c/go/+/267157
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
|
|
Some functions that required holding the heap lock _or_ world stop have
been simplified to simply requiring the heap lock. This is conceptually
simpler and taking the heap lock during world stop is guaranteed to not
contend. This was only done on functions already called on the
systemstack to avoid too many extra systemstack calls in GC.
Updates #40677
Change-Id: I15aa1dadcdd1a81aac3d2a9ecad6e7d0377befdc
Reviewed-on: https://go-review.googlesource.com/c/go/+/250262
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Trust: Michael Pratt <mpratt@google.com>
|
|
This change adds a global set of heap statistics which are similar
to existing memory statistics. The purpose of these new statistics
is to be able to read them and get a consistent result without stopping
the world. The goal is to eventually replace as many of the existing
memstats statistics with the sharded ones as possible.
The consistent memory statistics use a tailor-made synchronization
mechanism to allow writers (allocators) to proceed with minimal
synchronization by using a sequence counter and a global generation
counter to determine which set of statistics to update. Readers
increment the global generation counter to effectively grab a snapshot
of the statistics, and then iterate over all Ps using the sequence
counter to ensure that they may safely read the snapshotted statistics.
To keep statistics fresh, the reader also has a responsibility to merge
sets of statistics.
These consistent statistics are computed, but otherwise unused for now.
Upcoming changes will integrate them with the rest of the codebase and
will begin to phase out existing statistics.
Change-Id: I637a11f2439e2049d7dccb8650c5d82500733ca5
Reviewed-on: https://go-review.googlesource.com/c/go/+/247037
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
|
|
This change modifies the type of several mstats fields to be a new type:
sysMemStat. This type has the same structure as the fields used to have.
The purpose of this change is to make it very clear which stats may be
used in various functions for accounting (usually the platform-specific
sys* functions, but there are others). Currently there's an implicit
understanding that the *uint64 value passed to these functions is some
kind of statistic whose value is atomically managed. This understanding
isn't inherently problematic, but we're about to change how some stats
(which currently use mSysStatInc and mSysStatDec) work, so we want to
make it very clear what the various requirements are around "sysStat".
This change also removes mSysStatInc and mSysStatDec in favor of a
method on sysMemStat. Note that those two functions were originally
written the way they were because atomic 64-bit adds required a valid G
on ARM, but this hasn't been the case for a very long time (since
golang.org/cl/14204, but even before then it wasn't clear if mutexes
required a valid G anymore). Today we implement 64-bit adds on ARM with
a spinlock table.
Change-Id: I4e9b37cf14afc2ae20cf736e874eb0064af086d7
Reviewed-on: https://go-review.googlesource.com/c/go/+/246971
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
|
|
next_gc is mostly updated only during a STW, but may occasionally be
updated by calls to e.g. debug.SetGCPercent. In this case the update is
supposed to be protected by the heap lock, but in reality it's accessed
by gcController.revise which may be called without the heap lock held
(despite its documentation, which will be updated in a later change).
Change the synchronization policy on next_gc so that it's atomically
accessed when the world is not stopped to aid in making revise safe for
concurrent use.
Change-Id: I79657a72f91563f3241aaeda66e8a7757d399529
Reviewed-on: https://go-review.googlesource.com/c/go/+/246962
Trust: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
|
|
The history of pageAlloc using 's' as a receiver are lost to the depths
of time (perhaps it used to be called summary?), but it doesn't make
much sense anymore. Rename it to 'p'.
Generated with:
$ cd src/runtime
$ grep -R -b "func (s \*pageAlloc" . | awk -F : '{ print $1 ":#" $2+6 }' | xargs -n 1 -I {} env GOROOT=$(pwd)/../../ gorename -offset {} -to p -v
$ grep -R -b "func (s \*pageAlloc" . | awk -F : '{ print $1 ":#" $2+6 }' | xargs -n 1 -I {} env GOROOT=$(pwd)/../../ GOARCH=386 gorename -offset {} -to p -v
$ GOROOT=$(pwd)/../../ gorename -offset mpagecache.go:#2397 -to p -v
($2+6 to advance past "func (".)
Plus manual comment fixups.
Change-Id: I2d521a1cbf6ebe2ef6aae92e654bfc33c63d1aa9
Reviewed-on: https://go-review.googlesource.com/c/go/+/250517
Trust: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
|
|
Introduce GOOS=ios for iOS systems. GOOS=ios matches "darwin"
build tag, like GOOS=android matches "linux" and GOOS=illumos
matches "solaris". Only ios/arm64 is supported (ios/amd64 is
not).
GOOS=ios and GOOS=darwin remain essentially the same at this
point. They will diverge at later time, to differentiate macOS
and iOS.
Uses of GOOS=="darwin" are changed to (GOOS=="darwin" || GOOS=="ios"),
except if it clearly means macOS (e.g. GOOS=="darwin" && GOARCH=="amd64"),
it remains GOOS=="darwin".
Updates #38485.
Change-Id: I4faacdc1008f42434599efb3c3ad90763a83b67c
Reviewed-on: https://go-review.googlesource.com/c/go/+/254740
Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
|
|
This change uses the new offAddr type in more parts of the runtime where
we've been implicitly switching from the default address space to a
contiguous view. The purpose of offAddr is to represent addresses in the
contiguous view of the address space, and to make direct computations
between real addresses and offset addresses impossible. This change thus
improves readability in the runtime.
Updates #35788.
Change-Id: I4e1c5fed3ed68aa12f49a42b82eb3f46aba82fc1
Reviewed-on: https://go-review.googlesource.com/c/go/+/230718
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
|
|
Currently addrRange and addrRanges operate on real addresses. That is,
the addresses they manipulate don't include arenaBaseOffset. When added
to an address, arenaBaseOffset makes the address space appear contiguous
on platforms where the address space is segmented. While this is
generally OK because even those platforms which have a segmented address
space usually don't give addresses in a different segment, today it
causes a mismatch between the scavenger and the rest of the page
allocator. The scavenger scavenges from the highest addresses first, but
only via real address, whereas the page allocator allocates memory in
offset address order.
So this change makes addrRange and addrRanges, i.e. what the scavenger
operates on, use offset addresses. However, lots of the page allocator
relies on an addrRange containing real addresses.
To make this transition less error-prone, this change introduces a new
type, offAddr, whose purpose is to make offset addresses a distinct
type, so any attempt to trivially mix real and offset addresses will
trigger a compilation error.
This change doesn't attempt to use offAddr in all of the runtime; a
follow-up change will look for and catch remaining uses of an offset
address which doesn't use the type.
Updates #35788.
Change-Id: I991d891ac8ace8339ca180daafdf6b261a4d43d1
Reviewed-on: https://go-review.googlesource.com/c/go/+/230717
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
|
|
Currently the scavenger will reset to the top of the heap every GC. This
means if it scavenges a bunch of memory which doesn't get used again,
it's going to keep re-scanning that memory on subsequent cycles. This
problem is especially bad when it comes to heap spikes: suppose an
application's heap spikes to 2x its steady-state size. The scavenger
will run over the top half of that heap even if the heap shrinks, for
the rest of the application's lifetime.
To fix this, we maintain two numbers: a "free" high watermark, which
represents the highest address freed to the page allocator in that
cycle, and a "scavenged" low watermark, which represents how low of an
address the scavenger got to when scavenging. If the "free" watermark
exceeds the "scavenged" watermark, then we pick the "free" watermark as
the new "top of the heap" for the scavenger when starting the next
scavenger cycle. Otherwise, we have the scavenger pick up where it left
off.
With this mechanism, we only ever re-scan scavenged memory if a random
page gets freed very high up in the heap address space while most of the
action is happening in the lower parts. This case should be exceedingly
unlikely because the page reclaimer walks over the heap from low address
to high addresses, and we use a first-fit address-ordered allocation
policy.
Updates #35788.
Change-Id: Id335603b526ce3a0eb79ef286d1a4e876abc9cab
Reviewed-on: https://go-review.googlesource.com/c/go/+/218997
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: David Chase <drchase@google.com>
|
|
This change removes the concept of s.scavAddr in favor of explicitly
reserving and unreserving address ranges. s.scavAddr has several
problems with raciness that can cause the scavenger to miss updates, or
move it back unnecessarily, forcing future scavenge calls to iterate
over searched address space unnecessarily.
This change achieves this by replacing scavAddr with a second addrRanges
which is cloned from s.inUse at the end of each sweep phase. Ranges from
this second addrRanges are then reserved by scavengers (with the
reservation size proportional to the heap size) who are then able to
safely iterate over those ranges without worry of another scavenger
coming in.
Fixes #35788.
Change-Id: Ief01ae170384174875118742f6c26b2a41cbb66d
Reviewed-on: https://go-review.googlesource.com/c/go/+/208378
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Austin Clements <austin@google.com>
|
|
This change modifies the semantics of waking the scavenger: rather than
wake on any update to pacing, wake when we know we will have work to do,
that is, when the sweeper is done. The current scavenger runs over the
address space just once per GC cycle, and we want to maximize the chance
that the scavenger observes the most attractive scavengable memory in
that pass (i.e. free memory with the highest address), so the timing is
important. By having the scavenger awaken and reset its search space
when the sweeper is done, we increase the chance that the scavenger will
observe the most attractive scavengable memory, because no more memory
will be freed that GC cycle (so the highest scavengable address should
now be available).
Furthermore, in applications that go idle, this means the background
scavenger will be awoken even if another GC doesn't happen, which isn't
true today.
However, we're unable to wake the scavenger directly from within the
sweeper; waking the scavenger involves modifying timers and readying
goroutines, the latter of which may trigger an allocation today (and the
sweeper may run during allocation!). Instead, we do the following:
1. Set a flag which is checked by sysmon. sysmon will clear the flag and
wake the scavenger.
2. Wake the scavenger unconditionally at sweep termination.
The idea behind this policy is that it gets us close enough to the state
above without having to deal with the complexity of waking the scavenger
in deep parts of the runtime. If the application goes idle and sweeping
finishes (so we don't reach sweep termination), then sysmon will wake
the scavenger. sysmon has a worst-case 20 ms delay in responding to this
signal, which is probably fine if the application is completely idle
anyway, but if the application is actively allocating, then the
proportional sweeper should help ensure that sweeping ends very close to
sweep termination, so sweep termination is a perfectly reasonable time
to wake up the scavenger.
Updates #35788.
Change-Id: I84289b37816a7d595d803c72a71b7f5c59d47e6b
Reviewed-on: https://go-review.googlesource.com/c/go/+/207998
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
|
|
This change adds two bits of logic to the scavenger's pacing. Firstly,
it checks to make sure we scavenged at least one physical page, if we
released a non-zero amount of memory. If we try to release less than one
physical page, most systems will release the whole page, which could
lead to memory corruption down the road, and this is a signal we're in
this situation.
Secondly, the scavenger's pacing logic now checks to see if the time a
scavenging operation takes is measured to be exactly zero or negative.
The exact zero case can happen if time update granularity is too large
to effectively capture the time the scavenging operation took, like on
Windows where the OS timer frequency is generally 1ms. The negative case
should not happen, but we're being defensive (against kernel bugs, bugs
in the runtime, etc.). If either of these cases happen, we fall back to
Go 1.13 behavior: assume the scavenge operation took around 10µs per
physical page. We ignore huge pages in this case because we're in
unknown territory, so we choose to be conservative about pacing (huge
pages could only increase the rate of scavenging).
Currently, the scavenger is broken on Windows because the granularity of
time measurement is around 1 ms, which is too coarse to measure how fast
we're scavenging, so we often end up with a scavenging time of zero,
followed by NaNs and garbage values in the pacing logic, which usually
leads to the scavenger sleeping forever.
Fixes #38617.
Change-Id: Iaaa2a4cbb21338e1258d010f7362ed58b7db1af7
Reviewed-on: https://go-review.googlesource.com/c/go/+/229997
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Austin Clements <austin@google.com>
|
|
I took some of the infrastructure from Austin's lock logging CR
https://go-review.googlesource.com/c/go/+/192704 (with deadlock
detection from the logs), and developed a setup to give static lock
ranking for runtime locks.
Static lock ranking establishes a documented total ordering among locks,
and then reports an error if the total order is violated. This can
happen if a deadlock happens (by acquiring a sequence of locks in
different orders), or if just one side of a possible deadlock happens.
Lock ordering deadlocks cannot happen as long as the lock ordering is
followed.
Along the way, I found a deadlock involving the new timer code, which Ian fixed
via https://go-review.googlesource.com/c/go/+/207348, as well as two other
potential deadlocks.
See the constants at the top of runtime/lockrank.go to show the static
lock ranking that I ended up with, along with some comments. This is
great documentation of the current intended lock ordering when acquiring
multiple locks in the runtime.
I also added an array lockPartialOrder[] which shows and enforces the
current partial ordering among locks (which is embedded within the total
ordering). This is more specific about the dependencies among locks.
I don't try to check the ranking within a lock class with multiple locks
that can be acquired at the same time (i.e. check the ranking when
multiple hchan locks are acquired).
Currently, I am doing a lockInit() call to set the lock rank of most
locks. Any lock that is not otherwise initialized is assumed to be a
leaf lock (a very high rank lock), so that eliminates the need to do
anything for a bunch of locks (including all architecture-dependent
locks). For two locks, root.lock and notifyList.lock (only in the
runtime/sema.go file), it is not as easy to do lock initialization, so
instead, I am passing the lock rank with the lock calls.
For Windows compilation, I needed to increase the StackGuard size from
896 to 928 because of the new lock-rank checking functions.
Checking of the static lock ranking is enabled by setting
GOEXPERIMENT=staticlockranking before doing a run.
To make sure that the static lock ranking code has no overhead in memory
or CPU when not enabled by GOEXPERIMENT, I changed 'go build/install' so
that it defines a build tag (with the same name) whenever any experiment
has been baked into the toolchain (by checking Expstring()). This allows
me to avoid increasing the size of the 'mutex' type when static lock
ranking is not enabled.
Fixes #38029
Change-Id: I154217ff307c47051f8dae9c2a03b53081acd83a
Reviewed-on: https://go-review.googlesource.com/c/go/+/207619
Reviewed-by: Dan Scales <danscales@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
|
|
Currently, the scavenger is paced according to how long it takes to
scavenge one runtime page's worth of memory. However, this pacing
doesn't take into account the additional cost of actually using a
scavenged page. This operation, "sysUsed," is a counterpart to the
scavenging operation "sysUnused." On most systems this operation is a
no-op, but on some systems like Darwin and Windows we actually make a
syscall. Even on systems where it's a no-op, the cost is implicit: a
more expensive page fault when re-using the page.
On Darwin in particular the cost of "sysUnused" is fairly close to the
cost of "sysUsed", which skews the pacing to be too fast. A lot of
soon-to-be-allocated memory ends up scavenged, resulting in many more
expensive "sysUsed" operations, ultimately slowing down the application.
The way to fix this problem is to include the future cost of "sysUsed"
on a page in the scavenging cost. However, measuring the "sysUsed" cost
directly (like we do with "sysUnused") on most systems is infeasible
because we would have to measure the cost of the first access.
Instead, this change applies a multiplicative constant to the measured
scavenging time which is based on a per-system ratio of "sysUnused" to
"sysUsed" costs in the worst case (on systems where it's a no-op, we
measure the cost of the first access). This ultimately slows down the
scavenger to a more reasonable pace, limiting its impact on performance
but still retaining the memory footprint improvements from the previous
release.
Fixes #36507.
Change-Id: I050659cd8cdfa5a32f5cc0b56622716ea0fa5407
Reviewed-on: https://go-review.googlesource.com/c/go/+/214517
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
|
|
Currently, scavenging information is printed if the gctrace debug
variable is >0. Scavenging information is also printed naively, for
every page scavenged, resulting in a lot of noise when the typical
expectation for GC trace is one line per GC.
This change adds a new GODEBUG flag called scavtrace which prints
scavenge information roughly once per GC cycle and removes any scavenge
information from gctrace. The exception is debug.FreeOSMemory, which may
force an additional line to be printed.
Fixes #32952.
Change-Id: I4177dcb85fe3f9653fd74297ea93c97c389c1811
Reviewed-on: https://go-review.googlesource.com/c/go/+/212640
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
|
|
This change makes it so that we check whether scavAddr is actually
mapped before trying to look at the summary for the fast path, since we
may segfault if that that part of the summary is not mapped in.
Previously this wasn't a problem because we would conservatively map
all memory for the summaries between the lowest mapped heap address and
the highest one.
This change also adds a test for this case.
Change-Id: I2b1d89b5e044dce81745964dfaba829f4becdc57
Reviewed-on: https://go-review.googlesource.com/c/go/+/212637
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
|
|
Prior to this change, if the heap was very discontiguous (such as in
TestArenaCollision) it's possible we could map a large amount of memory
as R/W and commit it. We would use only the start and end to track what
should be mapped, and we would extend that mapping as needed to
accomodate a potentially fragmented address space.
After this change, we only map exactly the part of the summary arrays
that we need by using the inUse ranges from the previous change. This
reduces the GCSys footprint of TestArenaCollision from 300 MiB to 18
MiB.
Because summaries are no longer mapped contiguously, this means the
scavenger can no longer iterate directly. This change also updates the
scavenger to borrow ranges out of inUse and iterate over only the
parts of the heap which are actually currently in use. This is both an
optimization and necessary for correctness.
Fixes #35514.
Change-Id: I96bf0c73ed0d2d89a00202ece7b9d089a53bac90
Reviewed-on: https://go-review.googlesource.com/c/go/+/207758
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
|
|
Currently the page allocator bitmap is implemented as a single giant
memory mapping which is reserved at init time and committed as needed.
This causes problems on systems that don't handle large uncommitted
mappings well, or institute low virtual address space defaults as a
memory limiting mechanism.
This change modifies the implementation of the page allocator bitmap
away from a directly-mapped set of bytes to a sparse array in same vein
as mheap.arenas. This will hurt performance a little but the biggest
gains are from the lockless allocation possible with the page allocator,
so the impact of this extra layer of indirection should be minimal.
In fact, this is exactly what we see:
https://perf.golang.org/search?q=upload:20191125.5
This reduces the amount of mapped (PROT_NONE) memory needed on systems
with 48-bit address spaces to ~600 MiB down from almost 9 GiB. The bulk
of this remaining memory is used by the summaries.
Go processes with 32-bit address spaces now always commit to 128 KiB of
memory for the bitmap. Previously it would only commit the pages in the
bitmap which represented the range of addresses (lowest address to
highest address, even if there are unused regions in that range) used by
the heap.
Updates #35568.
Updates #35451.
Change-Id: I0ff10380156568642b80c366001eefd0a4e6c762
Reviewed-on: https://go-review.googlesource.com/c/go/+/207497
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
|
|
This change makes it so that waking up the scavenger readies its
goroutine without "next" set, so that it doesn't interfere with the
application's use of the runnext feature in the scheduler which helps
fairness.
As of CL 201763 the scavenger began waking up much more often, and in
TestPingPongHog this meant that it would sometimes supercede either a
hog or light goroutine in runnext, leading to a skew in the results and
ultimately a test flake.
This change thus re-enables the TestPingPongHog test on the builders.
Fixes #35271.
Change-Id: Iace08576912e8940554dd7de6447e458ad0d201d
Reviewed-on: https://go-review.googlesource.com/c/go/+/208380
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
|
|
Change-Id: I5b909df0fd048cd66c5a27fca1b06466d3bcaac7
GitHub-Last-Rev: 778c5d21311abee09a5fbda2e4005a5fd4cc3f9f
GitHub-Pull-Request: golang/go#35624
Reviewed-on: https://go-review.googlesource.com/c/go/+/207421
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
|
|
In scavengeOne's fast path, we currently don't check the summary for the
chunk that scavAddr points to, which means that we might accidentally
scavenge unused address space if the previous scavenge moves the
scavAddr into that space. The result of this today is a crash.
This change makes it so that scavengeOne's fast path only happens after
the check, following the comment in mpagealloc.go. It also adds a test
for this case.
Fixes #35465.
Updates #35112.
Change-Id: I861d44ee75e42a0e1f5aaec243bc449228273903
Reviewed-on: https://go-review.googlesource.com/c/go/+/206978
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
|
|
Before this CL, if max > min and max was unaligned to min, then the
function could return an unaligned (unaligned to min) region to
scavenge. On most platforms, this leads to some kind of crash.
Fix this by explicitly aligning max to the next multiple of min.
Fixes #35445.
Updates #35112.
Change-Id: I0af42d4a307b48a97e47ed152c619d77b0298291
Reviewed-on: https://go-review.googlesource.com/c/go/+/206277
Reviewed-by: Ian Lance Taylor <iant@golang.org>
|
|
CL 201765 activated calls from the runtime to functions in math/bits.
When coverage and race detection were simultaneously enabled,
this caused a crash when the covered+race-checked code in
math/bits was called from the runtime before there was even a P.
PS Win for gdlv in helping sort this out.
TODO - next CL intrinsifies the new functions in
runtime/internal/sys
TODO/Would-be-nice - Ctz64 and TrailingZeros64 are the same
function; 386.s is intrinsified; clean all that up.
Fixes #35461.
Updates #35112.
Change-Id: I750a54dba493130ad3e68a06530ede7687d41e1d
Reviewed-on: https://go-review.googlesource.com/c/go/+/206199
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
|
|
This change defines a maximum supported physical and huge page size in
the runtime based on the new page allocator's implementation, and uses
them where appropriate.
Furthemore, if the system exceeds the maximum supported huge page
size, we simply ignore it silently.
It also fixes a huge-page-related test which is only triggered by a
condition which is definitely wrong.
Finally, it adds a few TODOs related to code clean-up and supporting
larger huge page sizes.
Updates #35112.
Fixes #35431.
Change-Id: Ie4348afb6bf047cce2c1433576d1514720d8230f
Reviewed-on: https://go-review.googlesource.com/c/go/+/205937
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
|
|
For the most part, heap memstats are already updated atomically when
passed down to OS-level memory functions (e.g. sysMap). Elsewhere,
however, they're updated with the heap lock.
In order to facilitate holding the heap lock for less time during
allocation paths, this change more consistently makes the update of
these statistics atomic by calling mSysStat{Inc,Dec} appropriately
instead of simply adding or subtracting. It also ensures these values
are loaded atomically.
Furthermore, an undocumented but safe update condition for these
memstats is during STW, at which point using atomics is unnecessary.
This change also documents this condition in mstats.go.
Updates #35112.
Change-Id: I87d0b6c27b98c88099acd2563ea23f8da1239b66
Reviewed-on: https://go-review.googlesource.com/c/go/+/196638
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
|
|
This change removes the old page allocator from the runtime.
Updates #35112.
Change-Id: Ib20e1c030f869b6318cd6f4288a9befdbae1b771
Reviewed-on: https://go-review.googlesource.com/c/go/+/195700
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
|
|
This change integrates all the bits and pieces of the new page allocator
into the runtime, behind a global constant.
Updates #35112.
Change-Id: I6696bde7bab098a498ab37ed2a2caad2a05d30ec
Reviewed-on: https://go-review.googlesource.com/c/go/+/201764
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
|
|
Currently the runtime background scavenger is paced externally,
controlled by a collection of variables which together describe a line
that we'd like to stay under.
However, the line to stay under is computed as a function of the number
of free and unscavenged huge pages in the heap at the end of the last
GC. Aside from this number being inaccurate (which is still acceptable),
the scavenging system also makes an order-of-magnitude assumption as to
how expensive scavenging a single page actually is.
This change simplifies the scavenger in preparation for making it
operate on bitmaps. It makes it so that the scavenger paces itself, by
measuring the amount of time it takes to scavenge a single page. The
scavenging methods on mheap already avoid breaking huge pages, so if we
scavenge a real huge page, then we'll have paced correctly, otherwise
we'll sleep for longer to avoid using more than scavengePercent wall
clock time.
Unfortunately, all this involves measuring time, which is quite tricky.
Currently we don't directly account for long process sleeps or OS-level
context switches (which is quite difficult to do in general), but we do
account for Go scheduler overhead and variations in it by maintaining an
EWMA of the ratio of time spent scavenging to the time spent sleeping.
This ratio, as well as the sleep time, are bounded in order to deal with
the aforementioned OS-related anomalies.
Updates #35112.
Change-Id: Ieca8b088fdfca2bebb06bcde25ef14a42fd5216b
Reviewed-on: https://go-review.googlesource.com/c/go/+/201763
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
|
|
This change adds a "locked" parameter to scavenge() and scavengeone()
which allows these methods to be run with the heap lock acquired, and
synchronously with respect to others which acquire the heap lock.
This mode is necessary for both heap-growth scavenging (multiple
asynchronous scavengers here could be problematic) and
debug.FreeOSMemory.
Updates #35112.
Change-Id: I24eea8e40f971760999c980981893676b4c9b666
Reviewed-on: https://go-review.googlesource.com/c/go/+/195699
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
|
|
This change adds a scavenger for the new page allocator along with
tests. The scavenger walks over the heap backwards once per GC, looking
for memory to scavenge. It walks across the heap without any lock held,
searching optimistically. If it finds what appears to be a scavenging
candidate it acquires the heap lock and attempts to verify it. Upon
verification it then scavenges.
Notably, unlike the old scavenger, it doesn't show any preference for
huge pages and instead follows a more strict last-page-first policy.
Updates #35112.
Change-Id: I0621ef73c999a471843eab2d1307ae5679dd18d6
Reviewed-on: https://go-review.googlesource.com/c/go/+/195697
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
|
|
This change turns off the scavenger if there's less than one physical
page of work to do. If there's less than one phyiscal page of work
today, then the computed time for the work to be done will be zero,
resulting in a floating point division by zero.
This is bad on two accounts. On the one hand it could cause a fault on
some systems. On the other hand, it could cause the pacing computations
done by the scavenger to be nonsense. While this is generally harmless
in the case where there's a very small amount of work to do anyway (the
scavenger might just back off expontentially forever, or do some work
and immediately sleep, because there's not much of it to do), it causes
problems for the deadlock checker. On platforms with a larger physical
page size, such as 64 KiB, we might hit this path in a deadlock
scenario, in which case the deadlock checker will never fire and we'll
just hang.
Specifically, this happens on ppc64 trybot tests, which is where the
issue was discovered.
Fixes #34575.
Change-Id: I8677db539447b2f0e75b8cfcbe33932244e1508c
Reviewed-on: https://go-review.googlesource.com/c/go/+/203517
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
|
|
As a small step toward speeding up timers, restrict modification
of the timer.when field to the timer code itself. Other code that
wants to change the when field of an existing timer must now call
resettimer rather than changing the when field and calling addtimer.
The new resettimer function also works for a new timer.
This is just a refactoring in preparation for later code.
Updates #27707
Change-Id: Iccd5dcad415ffbeac4c2a3cf015e91f82692acf8
Reviewed-on: https://go-review.googlesource.com/c/go/+/171825
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
|
|
This changes fixes an oversight in wakeScavenger which would cause ready
to be called off of the system stack. This change makes it so that
wakeScavenger calls goready, which switches to the system stack before
calling ready.
Fixes #34773.
Change-Id: Icb13f180b4d8fdd47c921eac1b896e3dd49e43b3
Reviewed-on: https://go-review.googlesource.com/c/go/+/200999
Run-TryBot: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
|
|
There are currently two edges in the lock cycle graph caused by
scavenge.lock: with sched.lock and mheap_.lock. These edges appear
because of the call to ready() and stack growths respectively.
Furthermore, there's already an invariant in the code wherein
mheap_.lock must be acquired before scavenge.lock, hence the cycle.
The fix to this is to bring scavenge.lock higher in the lock cycle
graph, such that sched.lock and mheap_.lock are only acquired once
scavenge.lock is already held.
To faciliate this change, we move scavenger waking outside of
gcSetTriggerRatio such that it doesn't have to happen with the heap
locked. Furthermore, we check scavenge generation numbers with the heap
locked by using gopark instead of goparkunlock, and specify a function
which aborts the park should there be any skew in generation count.
Fixes #34047.
Change-Id: I3519119214bac66375e2b1262b36ce376c820d12
Reviewed-on: https://go-review.googlesource.com/c/go/+/191977
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
|
|
This change makes it so that the scavenge goal is defined primarily in
terms of heap_inuse at the end of the last GC rather than next_gc. The
reason behind this change is that next_gc doesn't take into account
fragmentation, and we can fall into situation where the scavenger thinks
it should have work to do but there's no free and unscavenged memory
available.
In order to ensure the scavenge goal still tracks next_gc, we multiply
heap_inuse by the ratio between the current heap goal and the last heap
goal, which describes whether the heap is growing or shrinking, and by
how much.
Finally, this change updates the documentation for scavenging and
elaborates on why the scavenge goal is defined the way it is.
Fixes #34048.
Updates #32828.
Change-Id: I8deaf87620b5dc12a40ab8a90bf27932868610da
Reviewed-on: https://go-review.googlesource.com/c/go/+/193040
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
|
|
Use the following (suboptimal) script to obtain a list of possible
typos:
#!/usr/bin/env sh
set -x
git ls-files |\
grep -e '\.\(c\|cc\|go\)$' |\
xargs -n 1\
awk\
'/\/\// { gsub(/.*\/\//, ""); print; } /\/\*/, /\*\// { gsub(/.*\/\*/, ""); gsub(/\*\/.*/, ""); }' |\
hunspell -d en_US -l |\
grep '^[[:upper:]]\{0,1\}[[:lower:]]\{1,\}$' |\
grep -v -e '^.\{1,4\}$' -e '^.\{16,\}$' |\
sort -f |\
uniq -c |\
awk '$1 == 1 { print $2; }'
Then, go through the results manually and fix the most obvious typos in
the non-vendored code.
Change-Id: I3cb5830a176850e1a0584b8a40b47bde7b260eae
Reviewed-on: https://go-review.googlesource.com/c/go/+/193848
Reviewed-by: Robert Griesemer <gri@golang.org>
|
|
This change adds physHugePageShift which is defined such that
1 << physHugePageShift == physHugePageSize. The purpose of this variable
is to avoid doing expensive divisions in key functions, such as
(*mspan).hugePages.
This change also does a sweep of any place we might do a division or mod
operation with physHugePageSize and turns it into bit shifts and other
bitwise operations.
Finally, this change adds a check to mallocinit which ensures that
physHugePageSize is always a power of two. osinit might choose to ignore
non-powers-of-two for the value and replace it with zero, but mallocinit
will fail if it's not a power of two (or zero). It also derives
physHugePageShift from physHugePageSize.
This change helps improve the performance of most applications because
of how often (*mspan).hugePages is called.
Updates #32828.
Change-Id: I1a6db113d52d563f59ae8fd4f0e130858859e68f
Reviewed-on: https://go-review.googlesource.com/c/go/+/186598
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
|
|
This change adds a background scavenging goroutine whose pacing is
determined when the heap goal changes. The scavenger is paced to use
at most 1% of the mutator's time for most systems. Furthermore, the
scavenger's pacing is computed based on the estimated number of
scavengable huge pages to take advantage of optimizations provided by
the OS.
The purpose of this scavenger is to deal with a shrinking heap: if the
heap goal is falling over time, the scavenger should kick in and start
returning free pages from the heap to the OS.
Also, now that we have a pacing system, the credit system used by
scavengeLocked has become redundant. Replace it with a mechanism which
only scavenges on the allocation path if it makes sense to do so with
respect to the new pacing system.
Fixes #30333.
Change-Id: I6203f8dc84affb26c3ab04528889dd9663530edc
Reviewed-on: https://go-review.googlesource.com/c/go/+/142960
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
|
